In the drilling or work-over of oil wells it is necessary to provide a "draw works," which is a mechanism powered by a motor mechanism having the capability of rotating the cable spools of winches to raise and lower heavy loads, such as the drill stem utilized for drilling oil wells. The cable from the spools is generally an extremely long length of cable, the free end of which is looped several times through a crown block at the top of the rig and traveling block to provide efficient mechanical advantage for adequate lifting capability for the drilling rig. When a heavy load is lowered with or held by a draw works mechanism, controlled lowering or holding is generally accomplished by means of a winch brake system. For example, a brake system is employed to slowly lower rotating drill pipe as a well is being drilled in order to control pressure exerted by the drill bit on the formation being drilled.
The cable spools of drilling rig draw works are generally provided with band type brake systems of the self-energized type which are tightened by friction forces as the brake is applied to enhance the braking capability of the brake mechanism. While the self-energizing feature of band brake systems enhances the braking capability thereof, it also creates a lost motion condition when it is desired to rotate the cable spool in the opposite direction. This feature frequently causes jarring of the draw works mechanism which is, of course, undesirable.
Band type brake systems for winches and the like are generally considered excessively expensive to service and maintain in proper operating condition because of the frequency of repair necessary and the amount of down time caused by repairs. Excessive maintenance expense is caused in part because the connecting links utilized to connect the brake bands to the brake system are subjected to continual wear as the brake bands are manipulated thereby requiring frequent servicing of the connecting links to ensure safe operation of the brake system. Moreover, replacement of worm brake bands is not only expensive but frequently requires a substantial period of down time for the brake band replacement or repair operation.
In view of recent developments in disc brake systems, it is considered generally advantageous to employ disc brake systems for virtually all types of winch mechanisms. To adapt conventional winch mechanisms with disc brake systems or to manufacture new winch mechanisms having disc brake systems has not been commercially feasible for a number of reasons until development of the present invention. If a disc brake system were constructed to act upon one or both of the flanges of a cable spool for a winch mechanism, the disc brake system would severely limit the amount of cable that could be received by the winch spool and might otherwise interfere with winding and unwinding of the cable from the spool. On drilling rigs, and in other environments as well, it is necessary because of the general lack of space, for the draw works to be as compact as possible. Accordingly, it is not practical, and in most cases not possible to enlarge the flanges of a winch spool in order to receive disc brake systems. Moreover, the width of the winch cable spool of a drilling rig draw works and the proximity of the winch spool to other structural elements of the drill works, typically prevents any winch design that would allow provision of a spool of sufficient length to incorporate a disc brake assembly. It is necessary therefore that a disc brake assembly for conventional winch mechanisms, be accommodated in no more space than is typically allowed for band type winch brake systems.
Although a disc brake system may be developed having a single disc applying a braking force to one side only of a winch spool flange, such structure is typically disadvantageous and in fact undesirable when the winch system must be of extremely heavy duty. For example, disc brake systems capable of providing adequate braking for a winch that supports up to 20,000 feet of heavy duty drill stem for example, could cause the flanges of the cable spool to yield or to become severely distorted. It is necessary, therefore, that an extremely heavy duty brake system of this nature be constructed in such manner that equal braking forces may be simultaneously applied to opposite sides of a brake disc.
It is accordingly a primary object of the present invention to provide a novel disc brake system for rotatable mechanisms such as cable spools or the like that is capable of providing greater braking capability than band type braking systems of equivalent dimension.
It is another object of the present invention to provide a novel disc brake system for rotatable mechanisms such as cable spools that is not subject to lost motion movement upon reversing the rotation of the cable spool.
An even further object of the present invention contemplates the provision of a novel disc brake system that employs floating brake shoes that establish full braking engagement with a brake disc to ensure smooth and efficient braking operation.
It is another object of the present invention to provide a novel disc brake system that may include a safety locking mechanism that is automatically actuated responsive to predetermined undesirable conditions to provide locking against rotation as long as the predetermined undesirable condition exists.
Among the several objects of the present invention is noted the contemplation of a novel disc brake system for cable spools such as might be employed in a drilling rig draw works and that may include a fluid cooling capability to prevent brake fade and to enhance the service life of the braking surfaces.
It is also an important object of the present invention to provide a novel disc brake system for cable spools that may be utilized to convert conventional band type cable spool brake systems to disc brake systems.
It is an even further object of the present invention to provide a novel disc brake system incorporating brake shoes that may be replaced simply and easily with minimum down time.
Other and further objects, advantages and features of the present invention will become apparent to one skilled in the art upon consideration of the writtten specification, the attached claims and the annexed drawings. The form of the invention, which will now be described in detail, illustrates the general principles of the invention but it is to be understood that this detailed description is not to be taken as limiting the scope of the present invention.